This invention relates to sampling and monitoring microscopic organisms and substances, and more particularly to a collection technique and collector apparatus for such sampling and monitoring efforts.
Nuclear power plants will become increasingly important as a source of electrical energy during the next few decades. The potential hazards derived from the use of plutonium in fast-breader reactors will increase as such facilities are built. It has been estimated that by the year 2000, about 2,700 megacuries of radioactive wastes in the United States will have to be sequestered and about 400 megacuries of transuranic alpha emitters will be part of that waste. Plutonium-239 will be an important constituent of these transuranic alpha emitters and, since its half-life is 24,390 years, it will be a potential hazard for many thousands of years. Therefore, it is important that research be conducted now to determine how environmental and biological factors influence the pathway of plutonium to man.
Plutonium deposited on soil is believed to consist primarily of insoluble particles and of polymers adsorbed on soil particles. Plutonium-containing particles resuspended from soil can enter man by inhalation or ingestion. The larger inhaled particles can be removed from the respiratory system by ciliary action and can then be transferred to the gastrointestinal tract for excretion. The smaller particles may be more dangerous because they can lodge in the pulmonary space where they may be assimilated or retained, thus presenting a continuous source of radiation to the surrounding tissue.
Plutonium originally deposited on soil may be ingested by man by eating contaminated plants or animal products, such as vegetables, meat, and milk. Animals may become contaminated with plutonium through the inhalation of resuspended particles, the ingestion of dust particles deposited on vegetation, the ingestion of soil particles with the food and by grooming, and the ingestion of plants, containing plutonium. The fraction of plutonium that can be assimilated by animals and man is of primary concern; therefore, the chemical nature of the ingested plutonium may be critical. It is probable that the plutonium absorbed by plant roots and translocated to a leaf will be more readily absorbed in the intestines than plutonium deposited on the leaf with resuspended dust.
Plants have been shown to assimilate plutonium from soil. The discrimination factor, defined as the ratio of plutonium disintegrations per minute per gram of dry plant material to the plutonium disintegrations per minute per gram of dry soil, has been reported to be on the order of 10.sup..sup.-4 to 10.sup..sup.-6. Experimental evidence indicated that the rate of plutonium uptake of ladino clover increased with time, resulting in an increase of plutonium incorporation. This increase was explained as possibly being due to the continuing development of the plant roots which increased the number of contact points between the roots and the plutonium particles combined with an increasing biological availability of plutonium. It was suggested that plutonium availability might be enhanced by chelating materials present in the coil.
Another possibility which is supported by experimental results is that soil microorganisms are involved in the transfer of plutonium from soil to plants. It is well known that soil microorganisms are responsible for the solubilization of insoluble mineral soil constituents, thus making them available for plant assimilation. Similar attacks of soil microorganisms on basically insoluble forms of soil-deposited plutonium could convert a certain fraction into a form which is available to plants, animals, and man. Transport studies of selected pollutants, especially actinides and other radionuclides, from growth media to microorganisms and their spores could therefore become an increasingly important technique as a way to determine biological availability of the pollutants by carrying out a few simple experiments. One such technique comprises collecting fungal spores which are then conveniently analyzed for the pollutant. However, most present techniques to collect aerial spores from microorganisms do not exclude contact of the spores with the growth media which results in contamination of the spore surfaces with pollutants from the growth media, leading to erroneous results. A technique which allows convenient spore collection under conditions that strictly exclude any contact with the media contaminated with pollutants would result in great savings in time and money when determining biological availability of such pollutants. Such a technique would especially be useful in the monitoring of pollutants in the vicinity of conventional and nuclear power plants, of nuclear fuel reprocessing facilities, and of metal processing operations.
Thus, in order to carry out the above-mentioned transport studies and to obtain the needed evaluation of the impact of soil microorganisms on the uptake of plutonium and other contaminants by plants, there is a need for more effective methods and apparatus for carrying out the necessary studies, particularly with respect to the determination as to whether soil microorganisms assimilate plutonium and other pollutants and, if so, to quantify the amounts assimilated.